#include <bits/stdc++.h>

using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int n,m,x[500005],y[500005],ct,u[500505];
vector<int>V[100005];
bool viz[500005];
inline void DFS(int l)
{
    int i=0,dim=V[l].size(),k;

    for(;i<dim;++i)
    {  k=V[l][i];
        if(!  viz[ k ]      )
    { viz[k]=1;
        DFS(x[k]+y[k]-l);
    }
    }
    u[++ct]=l;

}


int main()
{
    fin>>n>>m;
    int i,a,b,ok=1;
    for(i=1;i<=m;++i)
        { fin>>x[i]>>y[i];
            V[x[i]].push_back(i);
            V[y[i]].push_back(i);
        }
    for(i=1;i<=n;++i)
      if(V[i].size()%2==1 || V[i].size()==0)
      {ok=0; break;}

    if(ok==0)
        fout<<-1;
    else
    { DFS(1);
        for(i=1;i<ct;++i)
            fout<<u[i]<<" ";
    }

    return 0;
}